Soldiers in fracas on royal ship (9)
I believe the answer is:
freighter
'ship' is the definition.
(freighter is a kind of ship)
'soldiers in fracas on royal' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'in' means one lot of letters goes inside another.
'fracas' becomes 'fight'.
'on' is a charade indicator (letters next to each other).
'royal' becomes 'er' (I've seen this in other clues**).
're' inserted within 'fight' is 'freight'.
'freight'+'er'='FREIGHTER'
(Other definitions for freighter that I've seen before include "Cargo-carrying ship or plane" , "A plane carrying large load" , "Cargo ship" , "transport vessel" , "Cargo-ship" .)